The present invention relates to acidic catalyst compositions, their preparation, and use to synthesize, for example .alpha.,.beta.-unsaturated carboxylic acids, their functional derivatives, or olefinic oxygen-containing organic compounds.
It is known that olefinic compounds can be synthesized by reacting aldehydes or acetals with organic compounds containing carbonyl groups such as carboxylic acids, esters, aldehydes, and ketones. Such reactions can be illustrated by the following equations: ##STR1## It will be noted that equations 1 and 2 use formaldehyde or methylal, respectively, as alternative reactants. These are conventional reactants which are each associated with certain disadvantages depending on the choice of catalyst. Catalysts employed for the reactions of equations 1 or 2 can broadly be classified as basic or acidic. It is well known, that basic catalysts, when employed in conjunction with the reaction of equation 1, will cause disproportionation of formaldehyde to H.sub.2, CO.sub.2, and methanol, in accordance with the Cannizzaro reaction thereby reducing the selectivity of the reaction to desired products such as methylmethacrylate (MMA) and/or methacrylic acid (MA). In addition, the use of a basic catalyst also causes decarboxylation of the co-reactant carboxylic acid or ester thereof whether formaldehyde is employed as a reactant or not, thereby further reducing the selectivity to desired products. Furthermore when formaldehyde is manufactured in the vapor phase, it is adsorbed and dissolved in water to reduce its potential to polymerize. Methanol is also employed as a polymerization inhibitor. Consequently, formaldehyde is generally sold economically as a 35-45 wt. % mixture of the same with the remainder being water and methanol. The presence of such large amounts of water and methanol makes it difficult to economically achieve a concentrated reactant feed stream. In view of the disadvantages of the base-catalyzed formaldehyde based synthesis route, attempts have been made to replace formaldehyde with a less troublesome reactant such as dimethoxy methane, also known as methylal. However, when methylal is employed in conjunction with a base catalyst, conversion of methylal is very low. Such low conversions are believed to be attributable to the inability of the basic catalyst to efficiently hydrolyze the methylal to formaldehyde which in turn reacts with the carboxylic acid or ester co-reactant. This problem has been alleviated to some extent by the use of acid catalysts. However, even with conventional acid catalysts, the conversion of methylal is still well under 100%. Furthermore, it has been reported (see Albanesi et al discussed hereinafter) that certain acid catalysts also lead to decarboxylation of, for example, methylpropionate producing CO.sub.2 and dimethyl ether.
Obviously, the most efficient use of methylal would be to convert 100% thereof to MMA and/or MA while keeping co-reactant decarboxylation to a minimum. Such high efficiency reactions are difficult, however, to achieve in practice. A suitable and relatively economic alternative would be to produce reusable by-products which could be recycled in as efficient manner as possible. One reusable by-product from methylal is formaldehyde. However, when less than 100% conversion of methylal occurs, optimum use of process credits would necessitate recovery and recycle not only of formaldehyde, but also of unconverted methylal. This complicates the recycle procedure relative to the recycle of formaldehyde alone. Furthermore, if one seeks to recycle formaldehyde, the decomposition thereof to CO, and H.sub.2 must also be minimized. Similar considerations apply to the undesired decarboxylation reactions which also produce unusable products that cannot be recycled.
Accordingly, and in view of the above it would be of extreme economic significance if a catalyst could be developed which is capable of employing either methylal or formaldehyde as a reactant for the production of .alpha.,.beta.-ethylenically unsaturated products for carboxylic acids or their derivatives without, or with at least reduced, attendant undesirable side reactions which occur when employing conventional acidic or basic catalysts.
Various processes and catalysts have been proposed for the aforedescribed reactions.
For example, U.S. Pat. No. 3,100,795 describes the use of basic catalysts such as natural or synthetic (e.g. zeolites), alkali and alkaline earth metal aluminosilicates, as well as alkali and alkaline earth metal hydroxides supported on natural or synthetic aluminosilicates or silica gels, to catalyze the reaction between methanol, propionic acid, and formaldehyde to form methylmethacrylate. The conversion to methylmethacrylate based on formaldehyde is reported in Example 5 as 66% and the yield is reported as 99%, although such terms as conversion and yield are left undefined in this patent. Neither the catalysts of the present invention nor the method of its preparation are disclosed in this patent.
U.S. Pat. No. 3,840,588, assigned to Monsanto, describes the use of alkali metal hydroxides or oxides dispersed on a support having a surface area of 350 to 1000 m.sup.2 /gm. Suitable support materials include aluminas, thorias, magnesias, silica-aluminas, and silicates. In addition to hydroxides or oxides, other alkali metal compounds may be deposited on the support such as carbonates, nitrates, sulphates, phosphates, inorganic salts, acetates, propionates or other carboxylates. All of such supported catalysts are basic catalysts and no reaction between the catalysts and their supports is even alleged, simple impregnation procedures being employed for deposition. These catalysts are employed in the reaction of formaldehyde and saturated alkyl carboxylates to form .alpha.,.beta.-ethylenically unsaturated esters at temperatures of at least 400.degree. to 600.degree. C. A methylmethacrylate selectivity of 82 mole % at formaldehyde conversions of 98% are reported in this patent at a reaction temperature of 400.degree. C. and a space time yield of 490 L/hr (Table II, Run 7). However, at 430.degree. C. and higher space time yields of 960 L/hr (Example 1) the selectivity to methylmethacrylate of 92 mole % is obtained at a formaldehyde conversion of only 67%. At reaction temperatures below 400.degree. C., it is alleged that selectivities drop significantly, e.g., to below 40% (see FIG. 2) due to the Cannizzaro reaction (Col. 3, Lines 29 et seq). Moreover, water must be employed in the feed stream in strictly controlled amounts to obtain good selectivity. In the absence of water, formaldehyde conversion is negligible, and in the presence of too much water selectivity drops drastically. The required use of water necessitates the use of alcohols in the feed stream to suppress hydrolysis of the ester reactant and reduce the amount of ester in the reaction zone by acting as a diluent (see Col. 3, Lines 55 et seq) as well as complicating the overall process to implement strict control of the water content of the feed stream. This control of water content can be further complicated by the in-situ production of water in the reactor. Thus, selectivities and yields achieved in this patent are obtained at the sacrifice of simplicity of process design and overall process economics.
U.S. Pat. No. 3,933,888, assigned to Rohm and Haas Co., discloses the reaction of formaldehyde with an alkanoic acid or its ester in the presence of basic catalysts containing basic pyrogenic silica (e.g. SA of 150 to 300 m.sup.2 /g) alone or impregnated with activating agents which provide additional basic sites to the pyrogenic silica when calcined. Such activating agents include alkali and alkaline earth metal hydroxides, oxides, amides, and salts such as carbonates, oxalates phosphates, e.g., Na.sub.3 PO.sub.4, Na.sub.2 HPO.sub.4, KOCH.sub.3, Na.sub.4 SiO.sub.4. The identity, impregnation, and calcination procedures, of the activating agent is always selected to provide a basic catalyst. A molar ratio of alkanoic acid:formaldehyde:water:methanol of from 1:1:0.01:0 to 1:1:6:0.03 is disclosed. With a molar ratio of propionic acid:formaldehyde:water:methanol of 20:20:50:1 and a maximum of 34% conversion of formaldehyde and propionic acid to methacrylic acid and methylmethacrylate, selectivities (referred to in this patent as yields) to MA+MMA no greater than 69%, based on formaldehyde converted, or 80%, based on propionic acid converted, are achieved. When reacting methyl propionate with formaldehyde, water and methanol in the same molar ratio, the selectivity to MA+MMA based on a formaldehyde conversion of 25% is 63% (see Ex. 24). Furthermore, from the data of Table III in this patent, it can be calculated that for every 100 moles of formaldehyde in the feed, 34 moles thereof are converted to MA+MMA, and 45 moles thereof remain unreacted. About 21 moles of formaldehyde are unaccounted for.
U.S. Pat. No. 4,118,588, assigned to BASF, is directed to a process for synthesizing .alpha.,.beta.-ethylenically unsaturated acids or esters such as methacrylic acid and methylmethacrylate from the reaction of propionic acid and/or methylpropionate with dimethoxymethane (methylal) in the presence of catalysts (most of which are acidic) based on one or more salts selected from phosphates and silicates of: magnesium, calcium, aluminum, zirconium, thorium and titanium. Such salts can be used alone or together with oxides of the same aforedescribed magnesium et al metals, and additionally boric acid and/or urea. Thus, a typical acidic catalyst consists of aluminum phosphate, titanium dioxide, boric acid, and urea. Included within the list of 62 possible combinations of various materials are aluminum phosphate and aluminum silicate, or aluminum phosphate, aluminum silicate, and boric acid. Such catalysts can be modified with alkali and/or alkaline earth metal: carboxylates, oxides, silicates and hydroxides. The method of catalyst preparation includes mixing and heating the constituent components of the catalyst in water, evaporating the water and drying. Other methods are disclosed, such as forming a paste, or precipitation from an aqueous solution, but each of these alternate methods employs water as the liquid medium. The components of the catalyst are described at Col. 6, Lines 44 et seq, as being present in the catalyst as a mere mixture, as members of a crystal lattice, or in the form of mixed crystals. This patent therefore does not disclose a catalyst composition of the present invention wherein the components thereof have been reacted in a liquid organic medium to form an amorphous or substantially amorphous material, nor does it disclose the method of preparing such a catalyst. The highest conversion of methylal reported in this patent is 92% at a selectivity (referred to in the patent as yield) to MMA of 95% when employing catalyst of TiO.sub.2, AlPO.sub.4, H.sub.2 BO.sub.4, and urea, and a reaction time of 30 min. As described hereinafter at Comparative Example 1, such selectivities drop drastically when the reaction time is extended to 2.5 hours after discarding the first 15 minutes of product.
U.S. Pat. No. 4,147,718, assigned to Rohm GmbH, is directed to a method for making .alpha.,.beta.-unsaturated carboxylic acids and their functional derivatives, such as methacrylic acid and methylmethacrylate, from the reaction of methylal (dimethoxymethane) with propionic acid or its corresponding ester or nitrile, in the presence of a catalyst, which catalyst is a combination of silicon dioxide provided with basic sites (as described in U.S. Pat. No. 3,933,888) and aluminum oxide, which optionally may also be provided with basic sites in a similar manner. Aqueous impregnation procedures are employed for incorporation of the basic sites, and the resulting basic silicon dioxide and aluminum oxide components are merely then optionally mixed or arranged in separate layers. Thus, the acid catalysts of the present invention are not disclosed in this patent. The highest selectivity to MMA is 87.1% but at a conversion of propionic acid or methylpropionate of only 13.3% The highest conversion reported is 42% at a MMA selectivity of 78%.
U.S. Pat. No. 4,324,908, assigned to SOHIO, is directed to a promoted phosphate catalyst for use in synthesizing .alpha.,.beta.-unsaturated products, which catalyst requires the presence of at least one or more of Fe, Ni, Co, Mn, Cu, or Ag, as promoters in conjunction with phosphorus and oxygen. The catalysts of the present invention do not require the presence of such promoter metals in any form. The highest per pass conversion of methylal to MMA+MA is 52.9% at a methylal conversion of 97.6%.
Albanesi, G., and Moggi, P., Chem. Ind. (Milan) Vol. 63, p. 572-4 (1981) disclose the use of Groups 3, 4, and 5 metal oxides in unsupported, or SiO.sub.2 supported form, for the condensation reaction between the methyl hemiacetal of formaldehyde (CH.sub.3 OCH.sub.2 OH) and methylpropionate to form methylmethacrylates. Ten percent WO.sub.3 supported on SiO.sub.2 is reported as the best catalyst relative to other disclosed catalysts because the decomposition of formaldehyde to CO and CO.sub.2 and the decarboxylation of methylpropionate, occur least over this catalyst. However, the highest reported formaldehyde conversion when employing the tungsten catalyst is only 37.5%. Furthermore, it is disclosed that gamma-alumina, silica-alumina and molecular sieves tend to convert the hemiacetal of formaldehyde to dimethylether and formaldehyde which in turn tend to immediately decompose to CO and H.sub.2 above 400.degree. C. while in contact with these materials.
U.S. Pat. No. 4,275,052, by the inventor herein, is directed to a process for synthesizing a high surface area alumina support (e.g., 300 to 700 m.sup.2 /g) from organic solutions of aluminum alkoxides by the hydrolysis of these alkoxides with water. In accordance with this process, a first solution of an aluminum alkoxide dissolved in an organic solvent selected from ethers, ketones, and aldehydes, is mixed with a second solution comprising water and a similar organic solvent. The resulting material is dried and calcined, preferably in a water free environment, i.e., a dry gas, since the presence of water at these steps of the preparation will adversely affect the surface area of the alumina. The resulting alumina is used as a support or carrier material for catalytic components capable of promoting various hydrocarbon conversion reactions such as dehydrogenation, hydrocracking, and hydrocarbon oxidations. Conventional promoters are employed for such reactions including platinum, rhenium, germanium, cobalt, palladium, rhodium, ruthenium, osmium and iridium. Thus, the use of these aluminas to catalyze the synthesis of .alpha.,.beta.-unsaturated products is not disclosed. Furthermore, the reaction between aluminum alkoxide with other hydrocarboxides, such as a zirconium alkoxide, and an acidic phosphorus compound is also not disclosed.
U.S. Pat. No. 4,233,184 is directed to an aluminum phosphate alumina composition prepared by mixing and reacting in the presence of moist air, an aluminum alkoxide and an organic phosphate of the formula (RO).sub.3 PO wherein R is, for example, alkyl or aryl. The phosphorus of the resulting composition is alleged to be in the form of AlPO.sub.4 based on x-ray analysis, but in some preparations the amorphous nature of the product is said to make identification of the phosphorus species difficult. The amorphous nature of these samples is believed to be attributable to low calcination temperatures, e.g., below 600.degree. C. The mole ratio of alumina to aluminum phosphate will depend upon the mole ratio of aluminum alkoxide to organic phosphate employed in the synthesis and the amount of aluminum phosphate in the final product can range from 10 to 90% by weight. Mixed alumina-metal oxide-aluminum phosphates are also disclosed wherein a mixture of metal alkoxides can be employed. Thus, a SiO.sub.2 -Al.sub.2 O.sub.3 -AlPO.sub.4 can be prepared from a mixture of silicon alkoxide and aluminum alkoxide with an organic phosphate. However, from the description provided in this patent, it does not appear that the optional metal oxides (e.g. SiO.sub.2) added initially as metal alkoxides (e.g. silicon alkoxide) react with the organic phosphate. For example, silicon alkoxide is merely converted to the corresponding oxide, i.e., SiO.sub.2. This is confirmed at Col. 3, Lines 3, 18, and 22, and Examples 4 to 9 wherein the optional additional metals are reported as being present as WO.sub.3 (Examples 4 and 5) MoO.sub.3 (Example 6), SiO.sub.2 (Examples 7 and 8), ZrO.sub.2 (Example 9) (see also the characterization of Catalyst G, Table VI). The organic phosphates employed in preparing the catalysts of this patent do not possess an acidic hydrogen nor is an ether, aldehyde, or ketone or mixtures thereof employed as a solvent medium (note Example 5 of this patent employs an isopropyl alcohol organic phosphate mixture during the preparation procedure, alcohol alone being impermissible in the present invention) as required by the present invention. The resulting composition is employed as a catalyst or catalyst support for processes such as cracking, hydrocracking, isomerization, polymerization, disproportionation, demetallization, hydrosulfurization, and desulfurization. Use of the composition as a catalyst for the synthesis of .alpha.,.beta.-unsaturated products is not disclosed.
Alumina-aluminum phosphate-silica zeolite catalysts are disclosed in U.S. Pat. Nos. 4,158,621 and 4,228,036.
In view of the commercial importance of .alpha.,.beta.-unsaturated products, such as methylmethacrylate, there has been a continuing search for catalysts which can produce such products at improved conversions, selectivities, and/or yields. The present invention is a result of this search.